In mobile communications, to achieve higher data rates it is necessary to increase the transmission bandwidths over those that can be supported by a single carrier or channel. One way to increase the transmission bandwidth is through carrier aggregation (CA), or sometimes channel aggregation. By using carrier aggregation, it is possible to utilize more than one carrier and in this way increase the overall transmission bandwidth.
Carrier aggregation allows expansion of effective bandwidth delivered to a user terminal through concurrent utilization of radio resources across multiple carriers. Multiple component carriers are aggregated to form a larger overall transmission bandwidth. These channels or carriers may be in contiguous elements of the spectrum, or they may be in different bands.
Depending on the operational mode it can happen, that a mobile device including a radio transceiver can generate interference that interferes with its own receiver operation. One example is LTE carrier aggregation between bands 17 and 4, where at the same time the transmitter can be activated on band 17, while one of the receivers needs to receive in band 4. Unfortunately all transmitters generate the third harmonic. However, the third harmonic of band 17 TX is on the same frequency as the receiver of band 4 resulting in a degraded sensitivity or signal quality.
Current solutions to signal interference are increasing the filtering requirements, reducing the output power of the interferer, or optimizing the cross-coupling to minimize the interference. In using filtering, the filters will increase insertion losses at the transceiver output resulting in significantly higher current consumption. Additionally, this high isolation cannot be achieved on a printed circuit board, therefore cross-coupling will bypass all these filters.